Simple question, but baffles me....

How do ppi and dpi relate? I know what they are, but when you talk to a print house, everything is in dpi, and when you work in ps it's in ppi. I tell them I am creating stuff using 300ppi and they say ok, no problem. I guess my question is, If you use 300 ppi as your screen resolution, will that always mean the the print output will be 300dpi?

DPI is not the same as PPI, but its about as close a correlation to monitor/print differences that anybody can get. All printing (and scanning) devices output images different than pixels on a screen. Screen pixels are perfectly lined up with each other, whereas with ink dots on a page, they're more scattered. Not to mention that pixels are square while most physical printing devices print in circular dots.

Here's a good confusing article on the subject, which even brings up the terms SPI and LPI.

http://desktoppub.about.com/library/weekly/aa101800a.htm

I use the term SPI so rarely in my work that I really don't think of anything other than in terms of PPI and DPI. However, if you print stuff, you will be hearing a lot about LPI. At least I have.

Basically all I'm saying is that making something at 300ppi is close enough to 300dpi in print to not matter too much.

Much the same way that on screen CMYK documents are not the same as actual CMYK printing processes. Close, but not a perfect science.

Cool! thanks for the help MrBogus. I read a book by Adobe on print so I got the jist(sp?) of how printing works and how cmyk is printed, but they didnt talk much about the relationship between screen res and print res. That just cleared things up =)
The article seems to be exactly what I am looking for. thanks.

The problem with all the confusion is because so few people, INCLUDING people who call themselves professionals, make the distinction between p.p.i. and d.p.i. when speaking about resolution. I can understand it when home users make the mistake, but it's just bad practice when pro's do it.

Everyone who visits this forum with the intention of honing their craft in computer graphics needs to read the article linked above, and then to make it a practice to use the terms correctly. Also, it never hurts to take the time to educate anyone you work with regularly on the terms, so that when you're communicating ideas about a project you're both speaking the same language.

p.p.i and d.p.i. are apples and oranges.

I understand that they are not the same thing, but when you create an image or work on a photo in ps you dont create it in dpi, but the final output (if going to the printers) is in dpi. So it confused me (because no one, and yes including the print houses ever clarified the difference or connection between dpi and ppi).
Like in the article is talked about lpi they had this formula:

formula example
LPI x 2 = SPI 133 x 2 = 266 required SPI
typical project on uncoated paper stock
LPI x 1.5 = SPI 175 x 1.5 = 263 required SPI
typical project for a glossy magazine
LPI x 2 x % (size) = SPI 85 x 2 x 150% = 255 required SPI
newspaper photo to be enlarged 50% from original

This is basically what I am looking for. Some concrete way to relate the two. But in ppi and dpi. Does that make sense?
Mostly because I am creating in 300 ppi and I wanted to make sure that that was the proper screen resolution so when I saved my document and imported it in like pgmaker or illustrator and did the layout, will the resolution be high enough.
To make all this shorter, you work in ppi, always when you use a computer. You can't get around that. But print houses don't print in ppi. So is there a general guidline to follow so that you get the best resolution when you send your project to the printers?

Thanks u23 and Mrbogus. =)

Yeah, you're zeroing in on the important concept here, Marble.

When you're getting something ready for offset printing you need to know ahead of time what size linescreen the printer will be using. Then create your Photoshop document using the formulas you mentioned above, just substitute p.p.i for s.p.i. as you unit of measurement. Do you see s.p.i. as a choice in Photoshop?....No, you don't. There's a reason for that. S.P.I. is rather arcane and I've never spoken to anyone who uses that terminology.

(agrees with secret spi handshake!) That was the first for spi for myself.
So if I were to create something for a magazine stock printing, it would be safe to work in 263 ppi and the resolution would come out fine?

Thanks u23 I am beginning to feel like this is making sense. hehe. It is really amazing how people in the print houses don't answer that question. I have asked the few places we use and they kind of 'skirt' around the subject. I made my boss get me this book a while ago, "Adobes Print Publishing Guide" and it very clearly goes through how printing works - great book. But it didnt distinguish that one question that kept burning in my mind. ppi ppi ppi.

I have a quirky little question and some seriously grouchy commentary for all that have read this article by desktop publishing dot com: what the hell displays at 96 ppi?

In my 10 years of photoshop seminars, classes, conferences, and overall training I've never made a 96 ppi anything, and I've gotten by just fine. As far as I'm concerned, you have 72 ppi for display purposes. period. (Until someone shows me otherwise).

Also, while I'm yapping (this is gonna piss some folks off, I'm sure)

- I'd like to thank the author of that article for over-complicating things, wasting 3 pages out of a 5 page article, and making people feel overwhelmed, all in the name of....I don't know. (Utopian, I agree: if you're a pro, know the difference. Otherwise, just call it dpi or ppi, the rest of the world does.)

The highlight of that article for me was: "talk to your printer to find the LPI you should be using for each type of printing project." -Now, we have every photoshop amateur attempting to contact the Adobe User forums because they can't find the LPI button in Photoshop.

Not to mention, eliminated all aspects of the word "fun" in graphic design, because the amateur user now feels stupid and inadequate due to the slant of the article and the general "looking-down-the nose-at-you-little-idiot" tone of professional graphic designers.

Interesting to note: she failed to go into this interesting angle: different equipment and variables in workflows require individual methods, thus negating 50% of the article. And, viewing distance is the most important part of the printing process. The only sure-fire way to get great results is to test your equipment and find out what works for YOU, then set up a workflow for that. (Then, write an article and assume everyone uses the same).

Kids, you want to save some time? read this instead:

Printing your image? Figure out what dpi you need/want to print at. Scan at or higher than that number. (300 is good for HP products, 360 for EPSON, 99% of the time. - even if you're printing at 1440 or 720 dpi)

Online use? Scan or shoot at low resolution (72 dpi). Anything higher is a waste of data, time and resources.

Oh, and to the amateurs and professionals alike: please - slow down enough to enjoy designing. You draw pictures for a living, for crying out loud.

[*note:graphicsguy isn't usually this grumpy, I'm a pretty nice guy...really! ]

Haha! Man, ouch. Well to be more specific. I work with mostly one print house and I have really good communication with them. I know what resolution to use because he told me too, but not why do I use that resolution. You know. And yes depending on what kind of printing you use will determine what you do, but we don't send large run projects to our epson or hp printers that we bought at Home Depot (c), and a Cd doesnt print very high resolution unless you got lots of money.
I dont really see the concept of lpi and dpi as quite that simple. It is kind of nice to know a bit about what goes on at the print house so when you talk to the printers you can speak the same language and fix potential problems.
Oh yeah Graphics Guy, we are not all kids =)
Not mad. Just curious what made you so edgy?

I'm not really edgy, dude, I swear!!

I've met quite a few of these self-proclaimed industry "experts". - Hell, a bunch of them trained me! - Most of them are yuppie a$$holes who think everyone can afford the best equipment, and everyone who can't is completely insignifant.

about the article. good idea. bad approach. bad vibes. yuck.

sorry about the kid thing, I was in a hurry - I'm at work!